1. Field of the Invention
The present invention relates to an ink jet recording ink tank, employed for an ink jet recording apparatus that performs a recording operation by discharging a liquid, such as ink.
2. Description of the Related Art
Conventionally, ink tanks, employed to supply ink to the recording heads of apparatuses to record data on a variety of print media and other materials, can roughly be categorized as being one of two types, depending on the ink storage method used.
The first type is one wherein an ink tank, in which ink is stored, is incorporated within the main body of an apparatus, and a tube, for example, is employed as an ink supply path leading from the ink tank to a recording head.
The second type is one that employs an ink absorbent member, arranged so as to cover an entire ink tank, and that uses capillary force to draw in and retain ink, and the capillary force is balanced between the ink absorbent member and an ink discharge port in a recording head to maintain a meniscus at the ink discharge hole. According to this absorbent member ink tank type, the amount of ink held is smaller than the maximum capacity of the ink absorbent member, so that a gas-liquid interface is generated, between the ink and the air in the ink absorbent member, near an atmosphere communication hole, where there is no ink. Through capillary force at the gas-liquid interface, ink is retained within the ink absorbent member. Another ink tank that employs an ink absorbent member is a partitioned ink chamber type. As a well known ink tank that employs this method, there is one wherein a negative pressure generating member storage portion, where a negative pressure generating member is stored, and an ink holder, adjacent to the pressure generating member storage portion for storing ink, are connected by a communication path, and another path, for introducing air, is formed that is extended into the vicinity of the communication path (see U.S. Pat. No. 5,509,140).
Furthermore, focusing now on the dynamic surface tension of ink, a method according to which, for the stable discharge of ink, the dynamic surface tension between a discharge port and an ink chamber is balanced (see U.S. Publication No. 2004/0069183). What draws attention in this proposal is a relationship between a dynamic surface tension of 10 Hz, which corresponds to the rapid migration state of ink that is discharged from a discharge port, and the dynamic surface tension of 1 Hz in the slow migration state of ink, which corresponds to the amount of ink supplied through the discharge port of the ink chamber. According to this proposal, a difference between the dynamic surface tension of ink in the rapid migration state and the dynamic surface tension in the slow migration state is set equal to or smaller than 7 mN/m. By adjusting the dynamic surface tension difference, the dynamic surface tension having a high frequency at the discharge port and the dynamic surface tension having a low frequency in the ink chamber are balanced, in order to discharge ink stably. When these dynamic surface tensions are balanced, the stable discharge of ink droplets should be obtained.
There is another proposal related to ink for which a drying viscosity is 100 mPa·s or less, the dynamic surface tension for a lifetime of 10 msec is 45 mN/m or higher, and the dynamic surface tension for a lifetime of 1000 msec is 35 mN/m or lower (see U.S. Pat. No. 7,037,362).
Generally, ink employed for ink jet recording is designed in accordance with a requested recording characteristic or a fixing characteristic relative to a recording medium. Further, a capillary characteristic for determining an ink supply characteristic relative to the recording head of an ink tank and an ink retaining property during physical distribution are designated for an ink tank that includes an ink retention member, such as an ink absorbent member. One of the matters to be considered for an ink tank, such as the one described above, is a relationship between the amount of ink available for use in the ink tank (the amount of residual ink) and a static negative pressure. FIG. 1 is a graph illustrating a general transition of a relationship between the amount of ink available for use and a static negative pressure. It should be noted that “ink exhausted” in FIG. 1 represents a condition wherein no more ink is available for supply to a recording head. Based on the relationship, the affect the static surface tension of ink has on the characteristic of the ink tank can be studied.
First, ink having a low static surface tension provides a great permeation effect relative to the ink retention member. Therefore, the entire static negative pressure movement shown in FIG. 1 is shifted downward, as shown by arrow “H”, and a period is extended until a static negative pressure PB is reached, at which time the condition is “ink exhausted”. That is, a large amount of ink can be consumed before “ink exhausted”, and the use efficiency of ink before “ink exhausted” tends to be improved. However, the initial static negative pressure PE is lowered, and since a reduction in the initial static negative pressure (PE) tends to impart energy to the movement of ink occasioned by vibrations or a pressure reduction during physical distribution, a problem, such as a leakage of ink, may occur. On the other hand, ink having a high static surface tension provides a low permeation effect relative to an ink retention member. Therefore, overall, the static negative pressure movement illustrated in FIG. 1 is shifted upward, as shown by arrow “I”, and the initial static negative pressure PE is raised. Since an increase in the negative pressure PE inhibits the movement of ink occasioned by vibrations or the like during physical distribution, at the time of distribution, reliability tends to be increased. However, a period before the static negative pressure PE is reached, and at which “ink exhausted” occurs, is short, and the amount of ink used before “ink exhausted” tends to be reduced. That is, the efficiency with which ink is used before “ink exhausted” also tends to be reduced. Therefore, conventionally, the structure of the ink tank and the material and the form of the ink retention member are taken into consideration, and a balance is obtained between reliability, to counter shocks that occur during physical distribution, and efficiency, in the use of ink until “ink exhausted”.
Furthermore, for an ink tank that is integrally formed with an ink jet recording head, in addition to the above mentioned problems related to the reliability of the physical distribution process and the use efficiency of ink until “ink exhausted”, another problem encountered is related to coping with shocks caused by an ink jet head being mounted on an ink jet recording apparatus. That is, since ink in the ink retention member is moved when a shock occurs, a resulting phenomenon is that ink present at the discharge port of the recording head is drawn in toward the tank. The ink that was drawn in may be returned using a suction mechanism provided for the apparatus.
The problems related to acquisition of reliability during physical distribution and to efficient use of ink have been described for an ink tank integrally formed with an ink jet recording head, and for an ink tank provided as an individual item. In addition, the following problem is not yet fully understood, and a resolution method therefor has, as yet, not been proposed. That is, the problem is associated with an improvement in an injection property of ink that is injected into an ink tank, and the distribution state of the ink that has been so injected. This problem will now be described. A conventional ink tank shortcoming is one that becomes apparent during the injection of ink into an ink tank, in consonance with the static surface tension of ink. Since for ink having a low static surface tension a high permeation effect is provided, ink injection can be performed and completed in only a short period of time. However, because of the high permeation effect, ink permeates along the shape of an ink retention member, and in accordance with variances in the internal structure. As a result, after the ink retention member has been filled, the condition of the ink at certain locations within the ink retention member may differ. On the other hand, for ink having a high static surface tension, since the surface tension of the ink is usually higher than the interfacial tension of the ink retention member, and since relative to the ink retention member the ink permeation effect provided is low, a satisfactory amount of ink can not be acquired to fill the ink retention member.